[0001] This invention is in the field of methods and apparatus for coating a substrate with
a metal oxide coating by pyrolitic decomposition of a metal compound on the hot glass
surface. More particularly, the invention is in the field of hoods for applying protective
coating to hollow glass containers.
[0002] The desirability of applying protective coatings to glass in general and to the exterior
of hollow glass containers in particular has long been recognized. Such coatings,
which include those resulting from the application of tin, titanium and other metallic
compounds, or other heat-decomposable organometallic compounds, protect the glass
surface from damage such as from abrasion and scratches which cause a loss of tensile
strength of the glass containers. The need for high tensile strength in e.g., glass
containers is particularly acute when the containers are mass-produced, move rapidly
in close proximity along high-speed conveyor lines, and are subsequently filled with
carbonated beverages, beer, wine, foodstuffs, and the like which can produce gaseous
pressure within the container. Protective coatings are usually applied as the glass
articles, generally containers, emerge in a heated, fully-shaped condition from a
glassware-forming machine, that is, at the "hot" end of the system. The containers
are thereafter transported away from the forming machine by a conveyor. Temperatures
in excess of 400 degrees Centigrade (°C) exist at the surface of the glass containers,
such that when a heat-decomposable inorganic metallic or organometallic compound is
applied to those surfaces, the compound decomposes and is converted to a metallic-oxide
coating.
[0003] One well-known and previously widely used technique for applying a protective coating
to the hot glass containers calls for spraying the opposite sides of the containers
as they travel on a conveyor in single file through spray heads positioned for optimal
coating of the glass surface of a particular container. Receivers are positioned on
the opposite side of the conveyor in alignment with the respective spray heads. Pressurized
air or inert gas with the coating compound entrained therein is discharged from one
or a plurality of spray heads at a significant positive pressure, while the receivers
are usually maintained at a relatively low pressure. The resultant pressure differential
increases the velocity, and thus the effectiveness, of the coating-precursor compound.
Coating systems of this nature are disclosed,
inter alia, in United States Patent No. 3,516,811, to Gatchet, et al., and U.S. 3,684,469, to
Goetzer, et al.
[0004] Gatchet, et al. recognized that the deposition of a metallic-oxide coating on the
finish of the glass container passing on a conveyor through the open-sided coating
apparatus of the prior art was undesirable, as noted in column 3, lines 21-57 of U.S.
3,516,811. Gatchet, et al. relied upon spray heads producing a theoretically laminar
flow which would pass laterally across the width of the conveyor to control the location
as well as the uniformity of the metal-oxide deposit, as shown in Fig. 4 of that patent.
[0005] The above-described coating systems, however, are what may be termed "open-sided,"
and are thus adversely influenced by ambient conditions in the facility where the
glass containers are formed. The ambient conditions of prime concern are rapidly-moving
air currents, moisture in the air, and the potentially toxic and corrosive fumes and
pollutants being discharged from the spray heads. Air currents can cause turbulent
conditions at the spray heads, which can in turn result in a preferential or uneven
application of the protective coating. Some of the coating will therefore accumulate
on the bottle "finish", the term used in the industry to designate the closure region
of the bottle. The rapidly-moving air currents disrupt the laminar-flow patterns which
are theoretically possible with open-sided systems, and the capability for uniformly,
and consistently, applying the same thickness of coating is seriously reduced.
[0006] To compensate for air currents as described above, the systems are therefore operated
at higher pressures, and with the use of greater amounts of coating compound, than
would be required under quiescent conditions. The necessary result of process adjustments
such as these is the use of greater amounts of coating compound than required for
optimum economy.
[0007] The moisture in the hostile atmosphere described above causes hydrolysis loss, thus
rendering some of the compound unfit for its intended purpose. Further, the escape
of potentially toxic fumes into the atmosphere at the work place can constitute an
occupational health hazard, and may also be a violation of applicable law. These fumes
are also generally quite corrosive, and can attack various components of the glass
factory, such as, e.g., blowers, exhaust systems, conveyors and roofs, obviously leading
to increased plant-maintenance costs. Additionally, the efficiency of these open-sided
systems is low, since much of the relatively expensive coating compound is wasted.
[0008] A second, well-known, and widely employed technique for applying a protective coating
to hot glass containers relies upon a formed sheet-metal coating hood with spray heads
and associated receivers situated therein. The hood obviates many of the problems
associated with the open-ended spray systems discussed above. For example, it isolates
the glass containers from ambient conditions, and furnishes a controlled atmosphere
which enhances the coating operations. The hood includes an exhaust system which captures
most of the air-entrained coating compound not adhering to the containers, thus reducing
the problem of venting the system and minimizing the opportunity for the coating compound
to attack building components. Also, that hood can significantly raise the coating
efficiency of the systems, with attendant cost savings.
[0009] Coating hoods substantially representative of the prior art are disclosed in United
States Patent No. 3,819,404 to Scholes et al.; U.S. 3,933,457, to Scholes; and U.S.
4,389,234 to Lindner. The most recent patent to Lindner, et al. presents a coating
hood including a tunnel for allowing containers to pass therethrough, and a vertically
adjustable flat roof for accommodating containers of various sizes. At least two jet
slots are located in each sidewall, and at least two receivers or suction slots are
aligned therewith. The jet and suction slots are interspersed opposite each other
in each sidewall. The coating compound is introduced through at least one feed point,
and blowers secured to the sidewalls furnish an inner and an outer loop of high-velocity
air, of which the inner loop contains the coating compound, to the interior of the
hood. Baffles are situated in the flow path of the high-velocity air so that the jets
issuing from the jet slots are well defined, and thus better suited for their intended
function.
[0010] The problem addressed herein is to provide novel apparatus for coating glass articles.
[0011] In one aspect the present invention provides apparatus for coating of glass with
a metal oxide coating, e.g. by chemical vapour deposition (CVD) at atmospheric pressure,
characterised by having at least two sidewalls and a top part, forming a tunnel through
which hot glass articles pass; a circulating carrier gas in which a coating chemical
is evaporated, whereby a metal oxide film is formed on the surface of the glass articles;
means for circulating the carrier gas, there being blowing and suction channels in
the active part of the hood formed in such a way that no inner sidewall exists inside
the tunnel, other than the line contacts between the walls of adjacent blowing and
suction channels.
[0012] The blowing and suction channels with line contact facing the glass articles may
have openings between them through which cooling air passes.
[0013] Other preferred features are set out in the claims.
[0014] In another aspect, the invention provides apparatus for coating glass particles comprising
a hood defining a tunnel with a conveyor path through the tunnel along which hot glass
articles pass in use, means for circulating a gas carrying a coating chemical, and
blowing and suction channels provided in the hood at a coating region thereof so that
the gas can be circulated over the conveyor path to contact the glass articles, characterised
in that wall portions of the hood at the coating region comprise plural wall segments
whose surfaces taper towards the conveyor path to respective narrow edges facing the
conveyor path.
[0015] These wall segments may be provided between, or between parts of, channels for blowing
or sucking gas onto/from the conveyor path region.
[0016] The wall segments of the special type may be provided in the sides of the hood, and/or
the top of the hood.
[0017] By using wall segments of this tapering form, the heating of the surfaces of the
wall segments by heat emanating from the conveyor path and articles thereon can be
reduced. We have found that this can reduce in a surprisingly advantageous way the
formation of deposits on these surfaces during operation.
[0018] In a still further aspect, at least 50%, more preferably at least 75% and most preferably
substantially all of the sidewall area facing onto the coating or active region of
a coating hood is made up by wall surface inclined away from the conveyor path direction
going through the hood. The inclination is preferably steep; most preferably at least
45° and more preferably at least 60° away from the conveyor path direction.
[0019] Additionally or alternatively, such wall construction may be provided at the top
of the hood.
[0020] The prior art, and an embodiment of the invention, are now described in detail with
reference to the accompanying drawings:
Figure 1 shows a prior-art coating hood for bottles or jars, the hood having a flat
inner wall with vapour slots.
Figure 2 is a plan view taken along lines 2 - 2 of Figure 1.
Figure 3 is a plan view showing a coating hood embodying this invention, having an
inner-wall configuration designed to reduce inner surface temperature.
[0021] The present invention comprises apparatus for coating glass articles, the apparatus
having at least two side walls and a top part which form a tunnel through which hot
glass articles pass; a circulating carrier gas with a coating chemical is caused to
impinge on the glass surface, whereby a metal oxide film is formed on the surface
of the glass articles. The apparatus has means for circulating the carrier gas, with
blowing and suction channels in the active, or coating, portion of the hood being
formed in such way that there is no flat inner sidewall inside the tunnel, other than
line, or edge, contacts between the walls of adjacent blowing and suction channels,
the blowing and suction channels with line contact facing the glass articles having
openings between them through which cooling air can pass.
[0022] This invention is applicable to the common case of coating bottles using monobutyltinchloride
(MBTC); however, the apparatus described herein is applicable generally to the coating
of glass with films of tin oxide, titanium oxide or other single metal oxide, or with
a mixture of a plurality thereof, using organometallic compounds, metal halides or
other suitable compounds as the coating-chemical precursor.
[0023] In other embodiments of the invention, single or multiple air-circulating loops are
provided, cooling air is forced by a blower through openings between blowing channels
and between suction channels, and a liquid cooling medium is used to cool the suction
and blowing channels from the outside.
[0024] The present invention will be best understood by a brief initial discussion of a
coating hood of the prior art. Figures 1 and 2 show a partially schematic view of
a double-vapor-loop coating hood 100 for bottles according to United States Patent
number 4,389,234. Each vapor loop has blowing slots 101, and on the opposite side
of the conveyor, suction slots 102, which guide the circulating vapors at high velocity
against the passing bottles 103. The liquid coating chemical is fed to each side of
the hood through pipes 104 by blowers 105 from appropriate supply sources not shown
here, but known to those skilled in the art. Bottles coated in this type of hood using
MBTC receive a uniform tin oxide coating at a relatively low chemical consumption.
However, such hoods nevertheless require cleaning from time to time to remove crust
from the interior, in order to maintain proper coating efficiency. The blowing slots
101 and suction slots 102 have flat sides 106 facing the conveyor path. Under the
conditions of high temperature encountered in forming glass articles, sides 106 become
hot due to the radiation of substantial amounts of heat from the bottles 103.
[0025] In the coating application of the hood shown in Figure 1, the circulating vapors
can become quite hot, and as noted above in such cases, buildup of a metal oxide crust
is found on the inner walls of the hood and on the inside of suction slots 102.
[0026] Turning now to Figure 3, there is shown a double-loop coating hood 300 generally
similar to the high-efficiency conventional coating hood of the prior art, depicted
in Figures 1 and 2. It has surprisingly been discovered that by changing the configuration
of slots 101 and 102, a substantial improvement in the economy of production of glass
articles can be effected.
[0027] In Figure 3, the coating hood is indicated generally by 300. Blowing slots 101 and
suction slots 102 of Figures 1 and 2 are modified as shown for blowing slots 301 and
suction slots 302 in hood 300, the modification being shown as the elimination of
the flat side 106, such that the sidewalls 310 of the blowing slots 301 and suction
slots 302 taper inwardly and meet in vertical edges 312 in the interior of the hood.
Consequently, at the active or coating region of the hood, the sidewall adjacent the
conveyor path consists substantially entirely of surface which is steeply angled away
from the conveyor path direction.
[0028] As a result of the conformation of the blowing slots 301 and suction slots 302, thermal
radiation from the hot bottles is spread over the inner surfaces 314 of the walls
of the blowing and suction slots. Because the surface is significantly larger in area
than the inner-wall surface of the conventional coating hood of Figure 1, the radiation
energy per unit of wall surface is reduced to by a factor which is a function of the
ratio of the wall surface areas of the respective slots; in the case of the construction
shown, that factor is about one-third of the energy of the conventional hood. Therefore,
the inner surface temperature in the active part of the hood can be from about 50°C
to about 150°C lower than in a conventional hood. This has surprisingly been found
to causer appreciably lower crust buildup and therefore less need for cleaning.
[0029] Apart from the active coating zone, flat wall parts in the coating apparatus can
also be made from wedged wall parts as in the active zone, to reduce crust formation.
The same circumstance is true for the top part where a flat ceiling can be formed
of wedged parts. Those skilled in the art will now recognize that instead of vertical
slots with vertical walls, slots can be of any form with wall, ceiling or floor wedges
in any position, the desideratum being the presentation of edges to the ware, rather
than flat radiating surfaces. Further, the orientation of the wedges need not be uniform.
[0030] In a determination of the utility of the present concept, a coating hood as described
above was installed on a production line for glass bottles. The line was producing
beer bottles of 33 centiliters each, having a diameter of 66 millimeters (mm), a height
of 160 mm, and weighing 150 g. The production rate was 470 bottles per minute. The
coating hood had an overall length of 1.3 meters and a width of 160 mm. The length
of the active airflow zone was 900 mm.
[0031] The hood ran for eight weeks before being inspected. On opening the hood, no crust
formation was found. Some pieces of glass were removed from the suction slots, but
this was without effect on the operation
per se.
[0032] After another eight weeks of operation, the hood was inspected again and showed no
crust formation, but only a loose, dusty tin oxide powder, which was easily cleaned
out. Throughout the operation of the hood as described here, crust buildup, as generally
encountered with coating apparatus of the prior art as described with respect to Figures
1 and 2, was minimal, and downtime and cleanup was substantially less than with previous
hoods.
[0033] Modifications and improvements to the preferred forms of the invention disclosed
and described herein may occur to those skilled in the art who come to understand
the principles and precepts hereof.